1. Field of the Invention
This invention relates to a vehicle detecting apparatus for judging crowdedness in a parking lot from the state of vehicles being parked therein.
2. Prior Art
A conventional vehicle detecting apparatus, as shown in FIG. 1, is composed of a television camera 61, an A/D converter 62 for converting an output from the television camera to a digital signal, a multiple value image memory 63 for storing image information converted by the A/D converter 62, a road surface luminance detector 65 for detecting luminance of a part of the information corresponding to a road surface stored in the multiple-value image memory 62, a vehicle existence judging region setting unit 64 for setting a region along the border of a parking space for parking a vehicle in which the presence or the absence of a vehicle is judged and extracting stored information corresponding to the set region, a binary converting circuit 66 for converting multiple-value information stored in the memory 63 to binary data, a vehicle existence judging threshold value setting unit 67 for setting a threshold value for judging the existence of a vehicle, and a vehicle detector 68 for detecting a vehicle based on the threshold values.
The operation of the conventional vehicle detecting apparatus as shown in FIG. 1 will be next described.
An image signal including a parked vehicle picked up by the television camera 61, after being converted to a digital signal by the A/D converter 62, is stored in the multiple-value image memory 63.
In the road surface luminance detector 65, a single region only including a road surface such as a passage-way for vehicles or the like is selected, a variance of luminance data in that region is calculated, and a maximum value a of the variance and a luminance level b at that time are detected and outputted to the binary converting circuit 66. In the binary converting circuit 66, b+.sqroot.a and b-.sqroot.a are calculated as threshold values for binary conversion. If multiple-value data is larger than b+.sqroot.a or smaller than b-.sqroot.a, "1" is outputted, and otherwise "0" is outputted. The output is applied to the vehicle detector 68.
In the vehicle detector 68, the number of pixels set at "1" in the vehicle existence judging region preset by the vehicle existence judging region setting unit 64 is counted, and then it is examined whether or not the counted value exceeds the threshold value for vehicle existence judgment which has been set in the vehicle existence judgement threshold value setting unit 67, to output the presence or the absence of a vehicle within a parking space.
The conventional vehicle detecting apparatus as mentioned above is capable of detecting a vehicle having luminance lower than that of the road surface by setting the two threshold values having a range therebetween and setting a binary "1" to a pixel having luminance higher than the maximum value of the range, that is, the upper threshold value, or lower than the minimum value of the range, that is, the lower threshold value.
Since such a conventional vehicle detecting apparatus sets two threshold values for binary conversion with a range from b+.sqroot.a to b-.sqroot.a, a pixel having luminance within this range of the threshold values for binary conversion will not be extracted as characteristic. Stated another way, a vehicle, even if being parked in a parking space, will not be detected by the conventional vehicle detecting apparatus if the number of pixels having luminance within the two threshold values for binary conversion is larger than the number of pixels having luminance out of the two threshold values.